Method for evaluating refrigeration cycle performance

ABSTRACT

The present invention discloses a method for field testing refrigeration cycle equipment to evaluate condenser and evaporator performance.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit under all relevant U.S. statutes, including 35 U.S.C. 119 (e), of U.S. Provisional Application No. 60/875,237 filed Dec. 14, 2006, titled METHOD FOR DETERMINING EVAPORATOR AIRFLOW VERIFICATION in the name of Keith A. Temple, Todd Rossi and Changlin Sun.

The present application is a continuation-in-part of U.S. patent application Ser. No. 11/985,170 filed Nov. 14, 2007, titled METHOD FOR DETERMINING EVAPORATOR AIRFLOW VERIFICATION, in the name of Todd M. Rossi, Keith A. Temple and Changlin Sun, wherein U.S. application Ser. No. 11/985,170 claims benefit under 35 U.S.C. §119(e) to U.S. Provisional Application No. 60/859,158 filed Nov. 14, 2006, titled METHOD FOR DETERMINING REFRIGERATION AND AIRFLOW VERIFICATION in the name of Todd M. Rossi, Keith A. Temple and Changlin Sun.

U.S. Provisional Application No. 60/875,237, filed Dec. 14, 2006, is hereby incorporated by reference as if fully set forth herein.

U.S. patent application Ser. No. 11/985,170, filed Nov. 14, 2007, is hereby incorporated by reference as if fully set forth herein.

U.S. Provisional Application No. 60/859,158, filed Nov. 14, 2006, is hereby incorporated by reference as if fully set forth herein.

FIELD OF THE INVENTION

The present invention relates generally to cooling units (primarily refrigeration and air conditioning equipment) and more particularly to a method of providing a field test protocol for refrigeration cycle condenser and evaporator performance evaluation for existing residential and commercial HVAC units.

BACKGROUND OF THE INVENTION

In view of the rising costs of energy and the effects of global warming, it is the goal of certain government agencies and electric service providers to save energy and, in particular, electricity by improving the efficiency of equipment that utilizes electricity. The largest percentage of electricity generated in the United States is used to power lighting. The second largest percent of electricity generated in the United States is used to power Heating, Ventilation and Air Conditioning (HVAC) Systems.

With respect to lighting, there are two primary means of conserving energy, namely, replacing incandescent lights with fluorescent lights and urging consumers to turn off lights that are not needed. With respect to HVAC Systems, there are a number of ways to improve their efficiency, including maintaining optimal refrigerant charge, maintaining optimal airflow through the evaporators and condensers (by, for example, maintaining optimal fan speed and removing dust and residue from the evaporators and condensers).

Based on studies, it was determined that HVAC technicians do not (or are not trained to) finely tune refrigeration systems upon installation, and that proper charge in refrigeration systems tend to degrade over time. More disturbing was the fact that HVAC technicians did not understand the relationship refrigerant charge and air flow had on operating efficiency.

Two active players involved in improving HVAC efficiency are the California Energy Commission and the Southern California Edison Company. A program implemented in California and will likely be adopted by other states is the Refrigerant Charge and Airflow Verification Program (RCAVP).

Under the RCAVP, refrigeration systems in general, have their refrigerant charge and air flow verified and, if necessary, adjusted in order to improve efficiency and save energy. It was found that HVAC systems with TVX (thermostatic expansion valves) were just as likely as non-TVX systems to require adjustment to operate at peak or near-peak efficiency.

SUMMARY OF THE INVENTION

The present invention describes a method of evaluating the efficiency of condensers and evaporators in refrigeration cycle equipment. The method discloses setting up the refrigeration system, the testing setup, and protocols for the evaluations of both condensers and evaporators. The protocol can be applied to packaged or split systems, air-cooled air conditioning or heat pump systems, constant volume or variable volume indoor fans, and constant speed or variable speed compressors, single or tandem in circuit, including un-loaders.

The present invention also describes a series of calculations to be used in the evaluation, and identifies the point at which corrections will be necessary.

Kindly incorporate by reference, as if fully set forth herein, the following documents:

SCE Program: Attachment 1, Verified Charge and Airflow Services, Technical Specifications. CSG, 2006.

SDG&E Program: Attachment 2 HVAC Training, Installation & Maintenance Program Technical Specifications. KEMA, Nov. 22, 2006.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part of the specification, illustrate the embodiments of the present invention and, together with the following description, serve to explain the principles of the invention. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred, it being understood, however, that the invention is not limited to the specific instrumentality or the precise arrangement of elements or process steps disclosed.

FIG. 1A is the Title 24 ACM RD Table for determining Target Superheat;

FIG. 1B is a continuation of the Table shown in FIG. 1A;

FIG. 2 is the Title 24 ACM RD Table for determining Target Temperature Split;

FIG. 3A is a chart showing Target Evaporating Temperature, TxV Metering Device in accordance with the present invention; and

FIG. 3B is a chart showing Target Evaporating Temperature, Non-TxV Metering Device in accordance with the present invention.

FIG. 4 is a chart outlining the basic steps of the method and process according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In describing a preferred embodiment of the invention, specific terminology will be selected for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents that operate in a similar manner to accomplish a similar purpose.

1. OBJECTIVE

The method/process for providing a field test protocol for evaporator airflow verification on existing vapor compression cycle equipment will be disclosed. The primary steps in the subject method are presented in FIG. 4.

Attachment 1 titled VERIFIED CHARGE AND AIRFLOW SERVICES—TECHNICAL SPECIFICATIONS, and Attachment 2 titled HVAC TRAINING, INSTALLATION & MAINTENANCE PROGRAM—TECHNICAL SPECIFICATIONS which form a part of this disclosure provide some of the background for the problems and issues the present method addresses.

2. APPROACH 2.1. Refrigeration Cycle Condenser Evaluation

-   -   2.1.1 Evaluate each circuit individually using the Refrigeration         Cycle Condenser Evaluation protocol. The procedure is outlined         below; refer to the following sections for detailed         requirements.         -   2.1.1.1 Outdoor air damper closed (when applicable)         -   2.1.1.2 Circuit to be tested shall be operating fully             loaded.         -   2.1.1.3 Measure refrigeration cycle parameters and driving             conditions.         -   2.1.1.4 Evaluate condensing temperature over ambient (Tcoa)             relative to target value. If higher than threshold, unit is             eligible for condenser correction. Save Pre Test data for             each circuit.         -   2.1.1.5 If appropriate, service unit to improve condenser             performance. Save Post Test data for each circuit. Evaluate             change in Tcoa to determine if target improvement was             achieved.

2.2. Refrigeration Cycle Evaporator Evaluation

-   -   2.2.1 Evaluate each circuit individually using the Refrigeration         Cycle Evaporator Evaluation protocol. The procedure is outlined         below; refer to the following sections for detailed         requirements.     -   2.2.1.1 Outdoor air damper closed (when applicable)     -   2.2.1.2 Circuit to be tested shall be operating fully loaded.     -   2.2.1.3 Measure refrigeration cycle parameters and driving         conditions.     -   2.2.1.4 Evaluate evaporating temperature and superheat relative         to target values. Evaluate evaporator performance parameter and         if lower than thresholds, unit is eligible for evaporator         correction. Save Pre Test data for each circuit.     -   2.2.1.5 If appropriate, service unit to improve evaporator         performance. Save Post Test data for each circuit. Evaluate         change in evaporating temperature, change in superheat, and         change in evaporator performance parameter to determine target         improvement was achieved.

3. TEST SETUP 3.1. General Requirements for Refrigeration Cycle Performance Verification

-   -   3.1.1 This field protocol applies to the following existing         residential and commercial equipment:         -   3.1.1.1 Packaged or split system         -   3.1.1.2 Air-cooled air conditioning or heat pump system         -   3.1.1.3 Constant volume or variable volume indoor fan(s)         -   3.1.1.4 Constant speed or variable speed compressor(s),             single or tandem in circuit, including un-loaders     -   3.1.2 This field protocol does not apply to the following         equipment:         -   3.1.2.1 Systems with hot gas bypass control     -   3.1.3 Outdoor air damper should be closed (when applicable) and         return air damper open (100% return air). When closing the         outdoor air damper is not practical, testing may be completed         with the outdoor air damper at minimum position with no more         than approximately 20% outdoor air. The test configuration shall         be documented.     -   3.1.4 The indoor fan shall be operating at the nominal cooling         airflow rate.     -   3.1.5 For tests with one or more refrigeration circuits         operating, all condenser fans shall be operating at full speed.

4. REFRIGERATION CYCLE CONDENSER EVALUATION 4.1. General

-   -   4.1.1 Refrigeration cycle condenser evaluation shall be         completed for each independent refrigeration circuit     -   4.1.2 All compressors shall be operating fully loaded, for the         refrigeration circuit to be tested, for a minimum of 15 minutes         in cooling mode to reach quasi-steady operating conditions.         There shall be constant control inputs to fans and compressors.     -   4.1.3 This measure may be performed in conjunction with the         evaporator evaluation.     -   4.1.4 This measure shall be performed prior to any final charge         verification/adjustment.

4.2. Refrigeration Cycle Condenser Evaluation

-   -   4.2.1 Measurements: The following coincident measurements shall         be made, in accordance with section 1.6.5 of Attachment 1 (SCE         program) or section H.3.4 of Attachment 2, HVAC Program         Technical Specifications (SDG&E program), for the assessment of         the condenser performance:         -   4.2.1.1 Condenser entering air dry-bulb temperature             (Toutdoor, db)         -   4.2.1.2 Return air wet-bulb temperature (Treturn, wb)         -   4.2.1.3 Liquid line refrigerant pressure (Pcondenser) at the             condenser outlet (preferred) or discharge line refrigerant             pressure (Pdischarge) at the compressor outlet     -   4.2.2 Calculations and Criteria         -   4.2.2.1 If measuring discharge pressure instead of liquid             line pressure, calculate Pcondenser as Pdischarge minus 15             psi (or OEM specification for condenser pressure drop if             available).         -   4.2.2.2 Using the liquid line pressure (Pcondenser),             determine the condenser saturation temperature (Tcondenser)             from the standard refrigerant saturated pressure/temperature             chart.         -   4.2.2.3 Calculate condensing temperature over ambient (Tcoa)             as the condenser saturation temperature minus the condenser             entering air temperature. Tcoa=Tcondenser−Toutdoor.         -   4.2.2.4 Determine target value for condensing temperature             over ambient (Tcoa) from performance model, manufacturer's             data or use a default value of 25° F. If Tcoa is more than             12° F. greater than the target value, for any circuit, then             the unit is eligible for a condenser correction.         -   4.2.2.5 Save the Pre Test data for each circuit prior to             performing condenser correction or performing any other unit             service.         -   4.2.2.6 After completing condenser correction and any other             unit servicing, save Post Test data for each circuit.             Determine the improvement in Tcoa as the Pre Test Tcoa minus             the Post Test Tcoa for each circuit. If the capacity             weighted average improvement in Tcoa for the unit is greater             than or equal to 12° F. then all circuits qualify for the             condenser correction incentive. If the capacity weighted             average improvement in Tcoa for the unit is less than 12°             F., but one or more individual circuits have an improvement             in Tcoa greater than or equal to 12° F., the individual             circuits qualify for the condenser correction incentive.

5. REFRIGERATION CYCLE EVAPORATOR EVALUATION 5.1. General

-   -   5.1.1 Refrigeration cycle evaporator evaluation shall be         completed for each independent refrigeration circuit     -   5.1.2 All compressors shall be operating fully loaded, for the         refrigeration circuit to be tested, for a minimum of 15 minutes         in cooling mode to reach quasi-steady operating conditions.         There shall be constant control inputs to fans and compressors.     -   5.1.3 This measure may be performed in conjunction with the         condenser evaluation.     -   5.1.4 This measure shall be performed prior to any final charge         verification/adjustment.

5.2. Refrigeration Cycle Evaporator Evaluation

-   -   5.2.1 Measurements: The following coincident measurements shall         be made, in accordance with section 1.6.5 of Attachment 1 (SCE         program) or section H.3.4 of Attachment 2, HVAC Program         Technical Specifications (SDG&E program), for the assessment of         the evaporator performance:         -   5.2.1.1 Condenser entering air dry-bulb temperature             (Toutdoor, db)         -   5.2.1.2 Return air wet-bulb temperature (Treturn, wb)         -   5.2.1.3 Suction line refrigerant temperature (Tsuction) at             compressor suction         -   5.2.1.4 Suction line refrigerant pressure (Pevaporator) at             compressor suction     -   5.2.2 Calculations and Criteria     -   5.2.2.1 Using the suction line pressure (Pevaporator), determine         the evaporating (saturation) temperature (Tevaporator) from the         standard refrigerant saturated pressure/temperature chart.         -   5.2.2.2 Calculate Actual Superheat as the suction line             temperature minus the evaporator saturation temperature.             Actual Superheat=Tsuction−Tevaporator.         -   5.2.2.3 For a Non-TxV metering device, determine the Target             Superheat using FIGS. 1A and 1B, Table RD-2, of Attachment 1             (SCE program) or Table 1 of Attachment 2, HVAC Program             Technical Specifications (SDG&E program) or equivalent using             the return air wet-bulb temperature (Treturn, wb) and             condenser entering air dry-bulb temperature (Toutdoor, db).             If the test conditions are outside the range of the table,             then the test cannot be used under these conditions. For a             TxV metering device, the Target Superheat is 20° F. or the             manufacturer's recommended value.         -   5.2.2.4 Using the return air wet-bulb temperature (Treturn,             wb) and condenser entering air dry-bulb temperature             (Toutdoor, db), determine the target evaporating temperature             using (a) FIG. 3A, Table RD-4a, (b) FIG. 3B, Table             RD-4b, (c) OEM provided equivalent for unit being tested,             or (d) alternate method appropriate for unit being tested             that considers variation with return air wet-bulb             temperature (Treturn, wb) and condenser entering air             dry-bulb temperature (Toutdoor, db). If the test conditions             are outside the range of FIG. 3A (Table RD-4a) and FIG. 3B             (Table RD-4b), then the test cannot be used under these             conditions.         -   5.2.2.5 Calculate the difference (DTevap) between actual             evaporating temperature and target evaporating temperature.             DTevap=Actual Evaporating Temperature−Target Evaporating             Temperature.         -   5.2.2.6 Calculate the difference (DTsh) between actual             superheat and target superheat. DTsh=Actual Superheat−Target             Superheat.         -   5.2.2.7 For TxV metering device: if DTevap is less than             −8° F. (e.g., −12° F.) and DTsh is less than +5° F., for any             circuit tested, then the unit qualifies for an evaporator             correction.         -   5.2.2.8 For non-TxV metering device: Evaluate the evaporator             performance parameter Δ_(ec) using the equation provided             below. If Δ_(ec) is less than −7° F., for any circuit             tested, then the unit qualifies for an evaporator             correction.

Δ_(ec)=DT_(evap)+0.0075DT_(sh) ²+0.1DT_(sh)

-   -   -   5.2.2.9 Save the Pre Test data for each circuit prior to             performing evaporator correction or performing any other             unit service.         -   5.2.2.10 After completing evaporator correction and any             other unit servicing, save Post Test data for each circuit.             Calculate DTevap and DTsh for the Post Test data.         -   5.2.2.11 For TxV metering device: If the capacity weighted             average improvement (increase) in DTevap for the unit is             greater than or equal to 8° F. then all circuits qualify for             the evaporator correction incentive. If the capacity             weighted average improvement (increase) in DTevap for the             unit is less than 8° F., but one or more individual circuits             have an improvement greater than or equal to 8° F., then the             individual circuits qualify for the evaporator correction             incentive.         -   5.2.2.12 For non-TxV metering device: If the capacity             weighted average improvement (increase) in Δ_(ec) (i.e.,             Δ_(ec-past)-Δ_(ec-pre)) for the unit is greater than or             equal to 7° F. then all circuits qualify for the evaporator             correction incentive. If the capacity weighted average             improvement in Δ_(ec) for the unit is less than 7° F., but             one or more individual circuits have an improvement greater             than or equal to 7° F., then the individual circuits qualify             for the evaporator correction incentive.

6. EQUATIONS

-   6.1. Capacity weighted average (cwa) value is calculated for the     parameter X where n is the number of circuits at C is the nominal     cooling capacity.

$X_{cwa} = \frac{\sum\limits_{i = 1}^{n}{X_{{circuit}\text{-}i}C_{{circuit}\text{-}i}}}{\sum\limits_{i = 1}^{n}C_{{circuit}\text{-}i}}$

7. REFERENCES

-   7.1. SCE Program: Attachment 1, Verified Charge and Airflow     Services, Technical Specifications. CSG, 2006. -   7.2. SDG&E Program: Attachment 2 HVAC Training, Installation &     Maintenance Program Technical Specifications. KEMA, Nov. 22, 2006.

Although this invention has been described and illustrated by reference to specific embodiments, it will be apparent to those skilled in the art that various changes, modifications and equivalents may be made which clearly fall within the scope of this invention. The present invention is intended to be protected broadly within the spirit and scope of the appended claim(s). 

1. A method of testing a refrigeration system comprising: operate all compressors under full load in cooling mode for the refrigeration circuit to be tested; allow all compressors to reach at least a quasi-steady operating condition; measure the refrigeration cycle parameters; where the refrigeration cycle parameters include at least the condenser entering air dry-bulb temperature and the return air wet-bulb temperature are measured; where at least one of the liquid line pressure or the suction line pressure is measured; use one refrigeration cycle parameter to determine a temperature parameter; calculate at least one performance parameter; determine at least one target parameter and range; compare at least one performance parameter to the corresponding target parameter and range; determine whether the performance parameter falls outside the target parameter and range; and where if comparison fails then the system is eligible for correction.
 2. The method of claim 1 where the condenser saturation temperature is determined from the liquid line pressure; where the performance parameter is condensing temperature over ambient; where condensing temperature over ambient is calculated from the condenser saturation temperature and the condenser entering air dry-bulb temperature; and where the condensing temperature over ambient is compared to a corresponding target parameter.
 3. The method of claim 2 where the target parameter is determined from at least one of a performance model, manufacturer's data or a default value of 25° F.; and where if the condensing temperature over ambient is over about 12° F. from the target parameter, then the refrigeration circuit is eligible for correction.
 4. The method of claim 3 where the condenser performance is being evaluated.
 5. The method of claim 1 further comprising measuring suction line refrigerant temperature; and where the evaporator saturation temperature is determined from suction line pressure.
 6. The method of claim 5 further comprising calculating an actual superheat from the suction line refrigerant temperature and the evaporator saturation temperature; determining a target evaporator saturation temperature; and calculating a difference of evaporator saturation temperature (Dtevap) from evaporator saturation temperature and a target evaporator saturation temperature.
 7. The method of claim 6 further comprising; determining a target superheat; and calculating a difference of superheat (DTsh) from the actual superheat and the target superheat.
 8. The method of claim 7 where the evaporator system is being evaluated.
 9. The method of claim 8 further comprising determining whether a TxV metering device or a non-TxV metering device is being tested.
 10. The method of claim 9 where if the system has a TxV metering device, and the difference of evaporator saturation temperature (DTevap) is less than a predetermined value, such as −8 degrees F., and the difference of superheat (DTsh) is less than a predetermined value, such as 5 degrees F., then the system is eligible for correction.
 11. The method of claim 9 where an evaporator performance parameter (Epp) is calculated as a function of the parameters DTevap (difference of evaporator saturation temperature) and Dttsh (difference of superheat).
 12. The method of claim 11 where if the system has a non-TxV metering device, and the evaporator performance parameter (Epp) is less than a predetermined value, such as minus seven degrees Farenheit, then the system is eligible for correction.
 13. A method of evaluating the performance of a condenser in a refrigeration cycle machine, the method comprising the steps of: a) operate all compressors under full load in cooling mode for the refrigeration circuit to be tested; b) allow all compressors to reach at least a quasi-steady operating condition; c) measure condenser entering air dry-bulb temperature (Toutdoor, db); d) measure return air wet-bulb temperature (Treturn, wb); e) measure liquid line refrigerant pressure (Pcondenser) at the condenser outlet (preferred) or discharge line refrigerant pressure (Pdischarge) at the compressor outlet; f) if measuring the discharge pressure, calculate Pcondenser as Pdischarge minus 15 psi (or OEM specification for condenser pressure drop if available); g) using the liquid line pressure (Pcondenser), determine the condenser saturation temperature (Tcondenser) from the standard refrigerant saturated pressure/temperature chart; h) calculate condensing temperature over ambient (Tcoa) as the condenser saturation temperature minus the condenser entering air temperature (Tcoa=Tcondenser−Toutdoor); and i) determine target value for condensing temperature over ambient (Tcoa) from performance model, manufacturer's data or use a default value of 25° F. If Tcoa is more than a predetermined tolerance greater than the target value, such as 12 degrees F. greater, for any circuit, then the unit is eligible for a condenser correction.
 14. The method of claim 13 where the performance is further evaluated to include the impact of servicing, further comprising the following steps: j) save the Pre Test data for each circuit prior to performing condenser correction or performing any other unit service; and k) after completing condenser correction and any other unit servicing, save Post Test data for each circuit; l) determine the improvement in Tcoa as the Pre Test Tcoa minus the Post Test Tcoa for each circuit; and m) determining the capacity weighted average improvement in Tcoa for the unit as follows; i) for each circuit calculate the product of the individual circuit Tcoa improvement multiplied by the circuit nominal cooling capacity; ii) sum the circuit values; and iii) divide the sum by the total unit nominal cooling capacity. q) if the capacity weighted average improvement in Tcoa for the unit is greater than or equal to 12° F. then all circuits qualify for the condenser correction incentive. If the capacity weighted average improvement in Tcoa for the unit is less than 12° F., but one or more individual circuits have an improvement in Tcoa greater than or equal to 12° F., the individual circuits qualify for the condenser correction incentive.
 15. A method of evaluating the efficiency of an evaporator in a refrigeration cycle machine, the method comprising the steps of: a) operate all compressors under full load in cooling mode for the refrigeration circuit to be tested; b) allow all compressors to reach at least a quasi-steady operating condition; c) measure condenser entering air dry-bulb temperature (Toutdoor, db); d) measure return air wet-bulb temperature (Treturn, wb); e) measure suction line refrigerant temperature (Tsuction) at compressor suction; f) measure suction line refrigerant pressure (Pevaporator) at compressor suction; g) using the suction line pressure (Pevaporator), determine the evaporating (saturation) temperature (Tevaporator) from the standard refrigerant saturated pressure/temperature chart; h) calculate Actual Superheat as the suction line temperature minus the evaporator saturation temperature. Actual Superheat=Tsuction−Tevaporator; j) for a Non-TxV metering device, determine the Target Superheat using Table RD-2 of Attachment 1 (SCE program) or Table 1 of HVAC Program Technical Specifications (SDG&E program) or equivalent using the return air wet-bulb temperature (Treturn, wb) and condenser entering air dry-bulb temperature (Toutdoor, db). If the test conditions are outside the range of the table, then the test cannot be used under these conditions; h) for a TxV metering device, the Target Superheat is 20° F. or the manufacturer's recommended value; i) using the return air wet-bulb temperature (Treturn, wb) and condenser entering air dry-bulb temperature (Toutdoor, db), determine the target evaporating temperature using (a) FIG. 3A, Table RD-4a, (b) FIG. 3B, Table RD-4b, (c) OEM provided equivalent for unit being tested, or (d) alternate method appropriate for unit being tested that considers variation with return air wet-bulb temperature (Treturn, wb) and condenser entering air dry-bulb temperature (Toutdoor, db). If the test conditions are outside the range of FIG. 3A (Table RD-4a) and FIG. 3B (Table RD-4b), then the test cannot be used under these conditions; j) calculate the difference (DTevap) between actual evaporating temperature and target evaporating temperature (DTevap=Actual Evaporating Temperature−Target Evaporating Temperature); and k) calculate the difference (DTsh) between actual superheat and target superheat (DTsh=Actual Superheat−Target Superheat); l) calculate an evaporator performance parameter (Epp) as a function of the parameters DTevap (difference of evaporator saturation temperature) and DTsh (difference of superheat); and m) if the system has a TxV metering device, and the difference of evaporator saturation temperature (DTevap) is less than a predetermined value, such as −8 degrees F., and the difference of superheat (DTsh) is less than a predetermined value, such as 5 degrees F., then the system is eligible for correction; or if the system has a non-TxV metering device, and the evaporator performance parameter is less than a predetermined value, such as −7 degrees F., then the system is eligible for correction.
 16. The method of claim 15 where the performance is further evaluated to include the impact of servicing, the method further comprising the steps: n) save Pre test data for each circuit prior to performing evaporator correction or performing any other service on the unit, o) after completing any unit servicing, save Post test data for each circuit, p) if the system has a TxV metering device, determine the improvement in evaporator performance as the increase in DTevap from the Pre to the Post test; or if the system has a non-TxV metering device, determine the improvement in evaporator performance as the increase in Epp from the Pre to the Post test; q) determine the capacity weighted average evaporator improvement for the unit as follows, for each circuit calculate the product of the individual circuit improvement multiplied by the circuit nominal cooling capacity, sum the circuit values, and divide the sum by the total unit nominal cooling capacity. r) if the system has a TxV metering device, and the capacity weighted average improvement is greater than a predefined threshold, such as 8 degrees F., then all circuits qualify for an evaporator improvement incentive; if the capacity weighted average does not exceed the threshold, then only individual circuits with an improvement exceeding the threshold qualify for the incentive. s) if the system has a non-TxV metering device, and the capacity weighted average improvement is greater than a predefined threshold, such as 7 degrees F., then all, circuits qualify for an evaporator improvement incentive; if the capacity weighted average does not exceed the threshold, then only individual circuits with an improvement exceeding the threshold qualify for the incentive. 